Thin film amorphous silicon solar devices are useful for converting sunlight into electrical energy. In order for photovoltaic devices to be economically feasible and be used by the general public, it is advantageous to utilize methods and materials which are inexpensive, efficient and practical. There are literally hundreds of methods and inventions relating to various manufacturing techniques attempting to achieve commercial practicality. However, solar devices are complex systems and embody a myriad of parameters in their fabrication.
One of the important parameters is the amount of active area of the solar cell device which is exposed to the light, especially for large area a-Si solar cells. Electrical connections necessary for the operation of the device block the transmission of light into the active portions of the solar cell. The electrical connections are generally opaque and located between the light incident face and the active semiconductor material. To reduce active area loss, it is advantageous to minimize the area blocked by these electrical connections.
Furthermore, in the interest of commercial feasibility and to improve active area efficiency, it is advantageous to produce electrical connections which can be manufactured quickly, inexpensively and efficiently. The resultant electrical connections must have a sufficiently low resistance to conduct electricity through the cell. A problem arises with thinning the wires or grids used as electrical connections because resistance in a thinner wire is higher than in a thicker connection. Generally, minimizing the size of an electrical connection increases i.sup.2 R losses due to the increase in the resistance of the connection. Another problem is the quality of electrical contact at the interface with the conventional laser-scribing approach.
The U.S. Pat. No. 4,292,092 to Hanak discloses a laser-scribed, series-interconnected large area amorphous silicon (a-Si) solar cells. Although the scribed line can be thin, each subunit requires three scribed lines and a sufficient space between them to avoid electrical shorts. This results in a 9-31% active area loss of the solar cell panel.
In an attempt to improve the electrical connection interface, Hanak discloses a "laser punching" method in U.S. Pat. No. 4,532,371 issued July 30, 1985 to RCA Corporation. This patent to Hanak discloses a series-connected photovoltaic array wherein the series connection between a pair of adjacent photovoltaic cells comprises a plurality of "laser punched" openings extending through the semiconductor body with an electrical contact of one cell extending into the plurality of openings to provide a connection with an opposed electrical contact of the next adjacent cell.